Democratic presidential candidate Sen. Bernie Sanders stands with his wife Jane Sanders during a campaign rally Jan. 31 in Des Moines. (Evan Vucci/AP)

Billionaire hedge-fund managers and other wealthy donors gave millions to super PACs aligned with the 2016 presidential candidates in the second half of last year, fueling an intense slew of attacks that have dominated the Republican contest in recent weeks.

New federal campaign finance reports filed Sunday show that the GOP contenders continue to largely lean more heavily on their outside allies than do the Democratic candidates, who have focused on bringing in small contributions directly for their campaign committees.

On one end of the spectrum is financial executive Maurice “Hank” Greenberg, who gave $10 million through his company to Right to Rise USA, a super PAC backing former Florida governor Jeb Bush. The group brought in $118 million for the year — but only $15.1 million of that came in the second half of the year, demonstrating the extent to which donations have fallen off as Bush has struggled to gain traction.

On the other end are more than 1.3 million donors who have contributed small amounts to Sen. Bernie Sanders of Vermont, helping raise more than $20 million in January alone for his Democratic bid, according to his campaign.

“It’s a tale of two countries,” said David Donnelly, president of Every Voice, an advocacy group that seeks to reduce the influence of big donors on politics.

Altogether, the 12 remaining GOP candidates collected $90 million for their campaign committees in the last quarter of 2015. At the top was retired neurosurgeon Ben Carson, who brought in $22.6 million, followed by Sen. Ted Cruz (Tex.), who raised $20.5 million.

Sen. Marco Rubio (Fla.) collected $14.2 million, while real estate executive Donald Trump brought in $13.6 million. He lent his campaign $10.8 million and gave it another $113,000, part of the $2.8 million it raised in contributions.

Bush posted $7 million and Ohio Gov. John Kasich raised $3.2 million. New Jersey Gov. Chris Christie notched $2.9 million, former Hewlett-Packard chief executive Carly Fi­orina brought in $2.84 million and Sen. Rand Paul of Kentucky collected $2.1 million. Former Arkansas governor Mike Huckabee, former senator Rick Santorum and former Virginia governor Jim Gilmore were far behind, raising $703,000, $246,000 and $108,000 respectively.

Of them all, Cruz was best positioned financially heading into 2016. He had $18.7 million in the bank, while Rubio had $10.4 million, Bush had $7.58 million and Trump had nearly $7 million.

On the Democratic side, the three remaining candidates together raised $72.5 million in the last quarter of the year. Sanders came close to matching former secretary of state Hillary Clinton’s fundraising haul, raising $33.6 million to her $37 million. Clinton had $37.9 million on hand as the year began, while Sanders had $28 million. Former Maryland governor Martin O’Malley brought in $1.5 million and had less than $170,000 left in the bank.

 Sanders has been buoyed by more than 3.25 million contributions since he launched his campaign, including 770,000 in January, the campaign said. Because most were small sums, more than 99.9 percent of his donors have not yet reached the maximum $2,700 they can give to him for the primaries.

Jeff Weaver, Sanders’s campaign manager, said that the campaign is on pace to beat Clinton’s goal of raising $50 million in the first quarter of the year.

“Working Americans chipping in a few dollars each month are not only challenging but beating the greatest fundraising machine ever assembled,” he said in a statement.

While Sanders repeatedly boasts that he does not have an allied super PAC, he does have a network of independent groups supporting him, including a super PAC financed by National Nurses United, which reported raising $2.2 million in the last half of 2015.

The super PAC is financed by both mandatory and voluntary dues paid by its 185,000 members, officials told The Washington Post.

Meanwhile, Priorities USA Action, the main super PAC backing Clinton, announced Friday that it had raised $50.5 million through the end of January and had an additional $42 million in commitments.

Its biggest donor in the second half of 2015 was investor and philanthropist George Soros, who gave $6 million of the $25 million the super PAC brought it. Another $3 million came from Haim and Cheryl Saban, who have been the biggest individual lifetime supporters of Bill and Hillary Clinton.

A second pro-Clinton super PAC, Correct the Record, reported raising $2 million through the end of December, including a $1 million donation from Priorities USA.

Unlike other super PACs, Correct the Record coordinates directly with the Clinton campaign, relying on a 2006 Federal Election Commission ruling that declared that content posted online for free, such as blogs, is off limits to regulation.

On the GOP side, the diminished expectations for Bush could be seen in the dramatic fall-off of donations to Right to Rise. The super PAC, which initially sought to cap donations at $1 million early last year, raised just two contributions in that range after June: $10 million from Greenberg and $1 million from Morton Bouchard, the head of a Melville, N.Y., oil barge company.

So far, the group has plowed nearly $65 million of its haul into television spots, digital ads and mailers aimed at boosting Bush and attacking his rivals, making it by far the biggest independent spender of the 2016 presidential race.

In a distant second is Conservative Solutions PAC, which has shelled out more than $20 million in support of Rubio. The super PAC reported raising nearly $14.4 million between July and December, for a total haul of more than $30 million.

Wealthy hedge-fund managers Paul Singer and Kenneth C. Griffin each gave the group $2.5 million.

The super PAC also brought in $1 million apiece from David C. Humphreys, chief executive of a Joplin, Mo.-based roofing product company; Mary M. Spencer of Key Biscayne, Fla.; Cliff Asness, a New York hedge-fund manager; and Norman Braman, a billionaire car-dealership owner and former owner of the Philadelphia Eagles.

Braman, a longtime patron of Rubio, indicated last year that he was willing to give as much $10 million to support Rubio’s presidential bid. As of the end of December, he had given $6 million to the super PAC.

For his part, Cruz has been bolstered by more than half a dozen super PACs, which have reported spending nearly $10.6 million on his behalf.

The newest group, Stand for Truth, raised nearly $2.5 million between its formation in mid-November and the end of December.

The biggest share came from Adam Ross, a Dallas investor, and his wife, Tara, a writer and retired lawyer, who together gave $1 million.

A company in Park City, Utah, that appears to be linked to longtime Cruz donor Robert Marling of Spring, Tex., gave $250,000. The super PAC also got $250,000 from five business partnerships in Illinois.

Other major contributors in the last half of 2015 were hedge-fund billionaire Steve Cohen and his wife, Alexandra, who give $2 million to America Leads, the super PAC supporting Christie, bringing their total contributions to the group to $4 million.

Ohio Gov. John Kasich (R) got a boost from New York venture capitalist Michael Goguen, who gave $250,000 to his allied super PAC, New Day for America. The group got another $250,000 from Abigail Wexner, who is married to Leslie Wexner, founder of L Brands, and the same amount from a family trust in San Francisco.

Several major donors appeared to be hedging their bets, doling out large sums to super PACs supporting rival candidates.

Among them was Robert McNair, owner of the Houston Texans football team, who gave $500,000 to both the pro-Rubio Conservative Solutions PAC and Pursuing America’s Greatness, a super PAC backing former Arkansas governor Mike Huckabee. Billionaire investor Seth Klarman gave $300,000 to the pro-Christie group and $250,000 to the pro-Rubio super PAC.

Alice Crites contributed to this report.